devtools: Prevent crash when inspecting devtools:// page

Only in a debug build we can enter in the branch
"content::hasWebUIScheme" (:758) if the scheme is either "chrome://" or
"devtools://". Later, constructing the WebURILoader (in :772 before the
patch), there is the assumption that the uri scheme is always
kChromeUIScheme. This was causing me  crash of devtools while I was
trying to open it on a page under "devtools://devtools/...".
The crash was generated by web_ui_url_loader_factory.cc:254, where
`scheme_` was "chrome", while `request.url.scheme()` was "devtools"

Change-Id: If02ea147d494ed64c7f7dc560095f223c11f7dfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1687408
Commit-Queue: Nicolò Mazzucato <nicomazz@google.com>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676911}

chrome/browser/devtools/devtools_ui_bindings.cc

@@ -756,11 +756,12 @@ void DevToolsUIBindings::LoadNetworkResource(const DispatchCallback& callback,
         nullptr /* shared_cors_origin_access_list */);
     url_loader_factory = file_url_loader_factory.get();
   } else if (content::HasWebUIScheme(gurl)) {
+    content::WebContents* target_tab;
 #ifndef NDEBUG
-    // In debug builds, allow retrieving files from the chrome:// scheme
-    content::WebContents* target_tab =
-        DevToolsWindow::AsDevToolsWindow(web_contents_)
-            ->GetInspectedWebContents();
+    // In debug builds, allow retrieving files from the chrome:// and
+    // devtools:// schemes
+    target_tab = DevToolsWindow::AsDevToolsWindow(web_contents_)
+                     ->GetInspectedWebContents();
     const bool allow_web_ui_scheme =
         target_tab && content::HasWebUIScheme(target_tab->GetURL());
 #else
@@ -770,7 +771,8 @@ void DevToolsUIBindings::LoadNetworkResource(const DispatchCallback& callback,
       std::vector<std::string> allowed_webui_hosts;
       content::RenderFrameHost* frame_host = web_contents()->GetMainFrame();
       webui_url_loader_factory = content::CreateWebUIURLLoader(
-          frame_host, content::kChromeUIScheme, std::move(allowed_webui_hosts));
+          frame_host, target_tab->GetURL().scheme(),
+          std::move(allowed_webui_hosts));
       url_loader_factory = webui_url_loader_factory.get();
     } else {
       base::DictionaryValue response;